The evolution of cataclysmic and low-mass X-ray binaries

Abstract

We present an observational study of the structure and evolution of cataclysmic and low-mass X-ray binaries, concentrating on the 124 systems for which orbital periods are known. The eruptive properties and mass transfer rates of these stars are found to be highly correlated wit their orbital periods, suggesting that both the eruptive activity and the long-term evolution are determined by the properties of the lobe-filling secondaries. The secondaries do not satisfy the commonly used theoretical models of low-mass zero-age main-sequence (ZAMS) stars, but are, in general consistent with the empirically derived properties of the lower main sequence. We show stars, that R/R/sub direct-sum/ = (M/M/sub direct-sum/)/sup 0.88/ for low-mass ZAMS stars in the field, in wide binaries and in cataclysmic binaries. For masses above 0.8 M/sub direct-sum/, the empirical ZAMS is in reasonable agreement with the models. But in this regime (corresponding to orbital periods > or approx. = 9 hr), the secondaries in cataclysmic binaries are found to be slightly evolved from ZAMS.